The present invention concerns a device for detecting and quantitatively measuring the exposure of an object to a temperature at least equal to a predetermined temperature with account being taken of the duration of said exposure.
It applies especially, but not exclusively, to the checking of the integrity of the cold chain necessary for preserving certain objects or products, for example perishable foodstuffs, or even products for medical use, such as blood, vaccines or even temperature-sensitive medicines.
By way of example, it is known that a concentrate of red corpuscles can be preserved in a blood bank for forty-two days at a temperature of between +40° C. and +8° C. Once distributed by the blood transfusion service, this concentrate must be used very quickly if the ambient temperature exceeds +10° C. It is therefore important to know the moment when this temperature is exceeded and to measure for how long in order to know whether the concentrate is still usable.
A similar problem arises in the case of frozen products which must be preserved at a temperature of −30° C. and which, after de-frosting, must be consumed quickly.
Here again, it is important to detect whenever the preservation temperature is exceeded and, if necessary, the period for which it is exceeded, and the result of these two detections should be irreversible in character so that it can be ascertained long afterwards that the temperature has been exceeded as stated.
In an attempt to arrive at these results, electronic devices have already been proposed, employing a temperature measuring probe and a micro-controller making it possible both to detect when the temperature is exceeded and for how long. However, such a device proves too expensive to be used systematically on all the objects for which it is wished to monitor the temperature.
Attempts were also made to use temperature indicators employing fusible bodies changing state when a predetermined temperature is exceeded. These indicators, however, frequently inaccurate, do not take into account either by how much or for how long the temperature is exceeded, so that nothing makes it possible to indicate whether the object or the product remains usable or not.
The aim of the invention is therefore more particularly to eliminate these drawbacks by means of a device which detects the instances when the temperature is exceeded and which integrates into the time the amount by which the temperature is exceeded.